Hydrological feedbacks on peatland CH₄ emission under warming and elevated CO₂: A modeling study

Peatland carbon cycling is critical for the land–atmosphere exchange of greenhouse gases, particularly under changing environments. Warming and elevated atmospheric carbon dioxide (eCO₂) concentrations directly enhance peatland methane (CH₄) emission, and indirectly affect CH₄ processes by altering hydrological conditions. An ecosystem model ELM-SPRUCE, the land model of the E3SM model, was used to understand the hydrological feedback mechanisms on CH₄ emission in a temperate peatland under a warming gradient and eCO₂ treatments. We found that the water table level was a critical regulator of hydrological feedbacks that affect peatland CH₄ dynamics; the simulated water table levels dropped as warming intensified but slightly increased under eCO₂. Evaporation and vegetation transpiration determined the water table level in peatland ecosystems. Although warming significantly stimulated CH₄ emission, the hydrological feedbacks leading to a reduced water table mitigated the stimulating effects of warming on CH₄ emission. The hydrological feedback for eCO₂ effects was weak. The comparison between modeled results with data from a field experiment and a global synthesis of observations supports the model simulation of hydrological feedbacks in projecting CH₄ flux under warming and eCO₂. The ELM-SPRUCE model showed relatively small parameter-induced uncertainties on hydrological variables and their impacts on CH₄ fluxes. A sensitivity analysis confirmed a strong hydrological feedback in the first three years and the feedback diminished after four years of warming. Hydrology-moderated warming impacts on CH₄ cycling suggest that the indirect effect of warming on hydrological feedbacks is fundamental for accurately projecting peatland CH₄ flux under climate warming.